Modified von Mises

von_mises.py

def von_mises(S11, S22, S12, fc, ft):
    """
    Returns the type of failure according to the modified Von Mises
    failure criterion.

    Input
    -----
    S11 : float
        Normal stresses (σx)
    S22 : float
        Normal stresses (σy)
    S12 : float
        Shear stresses (τ)
    fc : float
        The compressive strength of the wall
    ft : float
        The tensile strength of the wall

    failure = 0 ----> No failure
    failure = 1 ----> Compression - Compression failure
    failure = 2 ----> Compression - Tension failure
    failure = 3 ----> Tension - Tension failure
    """
    failure = 0

    if S11 <= 0:
        if S22 <= 0: # S1
            if S11**2 + S22**2 - S11 * S22 + 3 * S12**2 - fc**2 >= 0:
                failure = 1
        else: # S4
            if S22 - S11 * ft / fc - ft >= 0:
                failure = 2
    else:
        if S22 <= 0: # S2
            if S22 - S11 * fc / ft + fc <= 0:
                failure = 2
        else: # S3
            if S11 + S22 - ft >= 0:
                failure = 3
    return failure